The present application relates to an aircraft power generation system, and specifically to detecting faulty rotating diodes within a rotating DC rectifier.
It is common in the aerospace industry to use a 3 phase synchronous generator to generate electrical power in an aircraft. A synchronous generator requires a rotating magnetic field to generate 3 phase voltages at its terminals. The rotating magnetic field is provided by a field winding carrying direct current (DC) current. The source for the DC current is provided by a 3 phase bridge rectifier which in turn is powered by exciter alternator. The exciter alternator is another synchronous machine that is excited by a stationary field winding current. An exciter field driver is used to control the exciter field current. The exciter field driver is part of a generator control unit. One of the functions of the generator control unit is to regulate the output voltage of the aircraft generator by controlling the exciter field current by means of the exciter field driver.
In an aircraft generator, failure of a shorted diode in the rotating bridge rectifier leads to loss of capacity to regulate the generator output voltage. This failure needs to be detected quickly to prevent further damage to the synchronous machine and any potential damage to the generator control unit that regulates the output voltage of the generator.
There are several methods in the prior art that can detect a shorted diode failure. These methods range from detecting loss of generating capacity to detecting ripple content in the exciter field current. However, these methods are relatively slow and, in aircraft generators that are designed to provide motoring function during engine start, a failed diode can be damaging to the generator control unit if not detected quickly.
Additionally, it is known that if a short circuit were to occur somewhere else in the circuit (such as in the load) it could skew the results of some detection methods and cause either false alarms, or a failure to recognize a faulty diode.